Make generateReferrerHeader() return a Referrer instead of a String

Source/core/loader/PrerenderHandle.cpp

Index: Source/core/loader/PrerenderHandle.cpp
diff --git a/Source/core/loader/PrerenderHandle.cpp b/Source/core/loader/PrerenderHandle.cpp
index 43a8619e1f4b0a3bf6eaad6f966b3f36d96c7148..f11bc14ae7d8045f6cfdab7665782894699676ce 100644
--- a/Source/core/loader/PrerenderHandle.cpp
+++ b/Source/core/loader/PrerenderHandle.cpp
@@ -46,14 +46,10 @@ PassOwnPtr<PrerenderHandle> PrerenderHandle::create(Document& document, Prerende
 {
     // Prerenders are unlike requests in most ways (for instance, they pass down fragments, and they don't return data),
     // but they do have referrers.
-    const ReferrerPolicy referrerPolicy = document.referrerPolicy();
-
     if (!document.frame())
         return PassOwnPtr<PrerenderHandle>();
 
-    const String referrer = SecurityPolicy::generateReferrerHeader(referrerPolicy, url, document.outgoingReferrer());
-
-    RefPtr<Prerender> prerender = Prerender::create(client, url, prerenderRelTypes, referrer, referrerPolicy);
+    RefPtr<Prerender> prerender = Prerender::create(client, url, prerenderRelTypes, SecurityPolicy::generateReferrer(document.referrerPolicy(), url, document.outgoingReferrer()));
 
     PrerendererClient* prerendererClient = PrerendererClient::from(document.page());
     if (prerendererClient)